The present invention relates to the field of wellbore cementing and completions. More particularly, the present invention relates to an improved apparatus for placing pipe downhole in a wellbore and for directing cement placement around the pipe exterior.
The production of oil and gas requires well tools, casing pipe, production tubing and other structures to be positioned downhole in a wellbore. Production tubing or pipe provides a conduit for transporting hydrocarbon fluids from the subsurface formation to the well surface. To prevent the migration of the hydrocarbon fluids around the pipe exterior, and to prevent the dilution of the hydrocarbon fluids with water produced from other strata, cement is placed in the annulus between the casing exterior and the wellbore wall.
To facilitate the formation of a uniform cement bond, pipe centralizers are installed on the pipe exterior to center the pipe in the wellbore so that cement is evenly distributed around the pipe. Centralizers are particularly useful in deviated and horizontal wells where the pipe rests against one side of the wellbore. In addition to the installation and bearing functions provided, centralizers restrict fluid channeling and cement voids by evenly distributing cement in the annulus between the pipe and the wellbore surface. The centralizers retain the tubular in the wellbore center so that cement can be pumped evenly in the annulus formed by the tubular and the wellbore surfaces.
Centralizers are connected to the exterior surface of casing pipe and other tubulars before the pipe is run downhole in a wellbore. Centralizers are attached to the tubular with set screws or with stop collars connected at either end of the centralizers. In other applications, a centralizer is placed between a stop collar and the enlarged pipe circumference of a pipe joint.
Various fixed and floating centralizers have been developed. Different centralizer types generally include flexible bow spring and solid body styles. As described in U.S. Pat. No. 3,762,472 to Alexander (1973), centered placement also inhibits tubular sticking as thousands of feet of tubular is run downhole in a wellbore.
Flexible spring centralizers have elastic ribs extending outwardly to contact the wellbore surface. Representative examples of flexible spring centralizers were illustrated in U.S. Pat. No. 4,938,299 to Jelsma (1990), which disclosed a centralizer having flexible blades for facilitating movement of the centralizer through deviated wellbore sections, and U.S. Pat. No. 5,261,488 to Gullet (1993), which disclosed a bow spring centralizer having the springs initially collapsed with a retainer band. U.S. Pat. No. 4,875,524 to Bradley et al. (1989) disclosed a semi-rigid floating spring type centralizer useful in horizontal or highly deviated wellbores.
Various centralizer type devices have been used to accomplish other functions downhole in a wellbore. U.S. Pat. No. 5,992,525 to Williamson et al. (1999) disclosed a spring member attached to a centralizer for preventing the centralizer from inadvertantly entering a lateral wellbore in a multilateral wellbore. U.S. Pat. No. 5,113,938 to Clayton (1992) disclosed an inflatable packer having an articulated whipstock attached below the packer for permitting sidetracks below the packer. U.S. Pat. No. 5,881,810 to Reinhold et al. (1999) disclosed a centralizer having two annular bands connected with a plurality of angled members. U.S. Pat. No. 5,358,039 to Fordham (1994) disclosed a centralizer having hinged spring blades for contacting the wellbore surface. U.S. Pat. No. 3,575,239 to Solum (1971) disclosed a bow spring centralizer having various springs for progressively contacting a restricted opening. In another use, U.S. Pat. No. 4,794,986 to Langer (1989) disclosed a reticulated centralizing device having muliple collars and bow springs. Additionally, U.S. Pat. No. 5,499,681 to White et al. (1996) disclosed a liner hanger for centering a liner within a wellbore.
Bow spring centralizers continuously exert forces against the wellbore wall, and these forces complicate pipe running operations. Such forces enhance the possibility of a pipe becoming stuck in the wellbore and must be overcome before the pipe can be rotated or reciprocated within the wellbore. Complications presented by flexible bow spring centralizers are particularly acute in deviated and horizontal wellbores.
Some of the spring centralizer disadvantages are eliminated by solid body centralizers. One example of a solid body centralizer was disclosed in U.S. Pat. No. 5,937,948 to Robbins (1999), wherein a centralizer was formed by extruding the centralizer body and extending blades. Various designs for solid body centralizers incorporate straight or angled blades having exterior surfaces for contacting the wellbore.
Regardless of whether a centralizer is bow spring or solid body design, different completion practices control whether a centralizer should be rigidly fixed to the pipe or should be free-floating relative to the pipe. During drilling of a wellbore, rotation of the drill bit creates a spiral micro-groove track in the wellbore wall. If a centralizer is rigidly attached to the pipe with set screws, adhesives, or other devices, movement of the pipe and centralizers against the wellbore wall generates torque adversely affecting the pipe. In geologic formations comprising shales or clays or unconsolidated sands, swelling and other factors create irregular wellbores having reduced diameters or ledges capable of preventing movement of the pipe. Wellbore discontinuities are also created at the junctures in multilateral wellbores. Additionally, fixed centralizers can destroy the mud filter cake distributed against the wellbore wall during drilling operations. Damage to such filter cake can lose wellbore circulation and can cause differential pipe sticking within the wellbore.
Because fixed centralizers can restrict pipe movement within the wellbore, free-floating bow spring or solid body centralizers can be installed between stop collars or between a single stop collar and a pipe joint. Stop collars are attached to the pipe exterior surface with multiple set screws turned through apertures in the stop collar frame. Stop collars permit the centralizer to rotate about the pipe and to move axially along the pipe longitudinal axis between the stop collars or pipe joints. In the absence of enlarged diameter pipe joints, two stop collars are required to restrict axial movement of a centralizer. Each stop collar prevents centralizer movement in one direction only and comprises an additional discontinuity in the pipe surface. Although stop collars and free-floating centralizers provide benefits in many applications, such systems increase the overall drilling costs because additional labor and parts can be required to install multiple stop collars on both sides of centralizers.
New wellbore drilling and completion technologies require changes in conventional centralizer practices. Complex wellbore completions systems in different zones and multi-branch wellbores encourages the deployment of multiple tool systems within a single wellbore section. Long horizontal wellbore branches require numerous centralizers distributed over the wellbore length, and conventional centralizers and associated stop collars are not practical in certain horizontal wellbore applications. Accordingly, a need exists for an improved apparatus for centralizing pipe within a wellbore and for distributing cement around the pipe.
The present invention provides a centralizer for engagement with a pipe exterior surface to be positioned downhole in a wellbore. The centralizer comprises a collar, at least one connector for attaching the collar to the pipe exterior surface, and a body engaged with the collar for containing axial movement of the body within a selected portion of the pipe exterior surface while facilitating rotational movement of the body relative to the pipe exterior surface. The body is further configured to selectively position the pipe relative to the wellbore.
In various embodiments of the invention, the connector can comprise a plurality of set screws, the body can comprise a first ring and a second ring connected by at least two ribs, and the ribs can be straight or angled relative to the longitudinal axis of the pipe.
A plurality of set screws can cooperate with a collar to retain the collar in fixed engagement with the pipe. The body can comprise a cage body forming a space for permitting installation of said collar within said space to limit axial movement of said body within a selected portion of said pipe exterior surface while facilitating rotational movement of said body relative to the pipe exterior surface. A lock can prevent axial or rotational movement of the body relative to the collar.